Oven 170°C Fan Bake. Then line the base and sides of a Swiss roll tin (approx. 20 x30cm) with baking paper.
Whisk the eggs and salt on medium speed until foamy, this will take about 2 minutes. Slowly add the sugar a few tablespoons at a time, counting to five between additions, then once half has been added you can slowly pour in the rest. Beat for 5-6 minutes until you can form a figure 8 on top of the eggs without it collapsing.
Whisk the olive oil, buttermilk, vanilla, lemon zest and juice. Fold this into the eggs.
Mix the flour, nuts and baking powder together with a whisk and fold in.
Bake in the centre of the oven for 20 - 25 minutes. After 20 minutes, insert a skewer for 1 second and check to make sure there’s no uncooked batter – it should come out clean.
Cool in the tin before removing and inverting on a cake rack as the cake is fairly light.
Cut into the shapes you want, in this case 7-9 cm rounds. Because you’ll be covering the cake with puree and ice cream, and the meringue, you can actually patch the offcuts together and have very little wastage.